Challenge begins to exhibit the world’s oldest working computer

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Public gets a chance to sponsor the restoration of the Harwell / WITCH computer at TNMOC

Click here to see the arrival of the Harwell / WITCH computer on BBC News Online

The historic Harwell computer, later known as the WITCH computer, comes out of storage this week to travel to The National Museum of Computing at Bletchley Park where it is planned to restore it to full working condition. Once restored by the volunteers at the Museum, it will be the oldest original functioning electronic stored program computer in the world and will be housed alongside the rebuild of Colossus Mk II, the world’s first electronic computer.

TNMOC is inviting members of the public and industry to [sponsor the restoration of the Harwell computer by purchasing one of 25 shares at £4500 each. The funds will be used by TNMOC, a registered charity, to undertake the restoration and extend the ever-expanding museum. (, international designer of software to optimize business processes, has become the first sponsor of the Harwell/WITCH computer restoration project.

The Harwell Computer dates back to 1949 when plans were drawn up for a machine to perform calculations then done by a team of bright young graduates using mechanical calculators. The team’s work had been so tedious that mistakes were inevitable, so the aim was to automate the work. Simplicity, reliability and un‐attended operation were the design priorities. Speed was a lower priority concern. The machine first ran in 1951.

Kevin Murrell, a director and trustee of TNMOC, explained: “The machine was a relay-based computer using 900 Dekatron gas-filled tubes that could each hold a single digit in memory -- similar to RAM in a modern computer -- and paper tape for both input and program storage.

“Its promises for reliability over speed were certainly met – it was definitely the tortoise in the tortoise and the hare fable. In a race with a human mathematician using a mechanical calculator, the human kept pace for 30 minutes, but then had to retire exhausted as the machine carried on remorselessly. The machine once ran for ten days unattended over a Christmas/New Year holiday period.”

The computer was operational at Harwell until 1957, when it was offered in a competition for colleges to see who could make best use of it. Wolverhampton and Staffordshire Technical College (later becoming Wolverhampton University) won and, then becoming known as the WITCH (Wolverhampton Instrument for Teaching Computing from Harwell), it was used in computer education until 1973. After a period on display at Birmingham Science Museum, it was disassembled and put in storage at Birmingham City Council Museums’ Collection Centre. Their curatorial care and attention means it can still be made to work again.

Its arrival at TNMOC on 3 September will be the first stage in an expected year-long restoration challenge.

The restoration project is under the aegis of the Computer Conservation Society, who have a long history of successful similar projects. “The TNMOC team of engineers is eager to start the restoration work,” continued Kevin Murrell. “They have proved their skills, perseverance and sheer ingenuity in many projects and for most of them this will be the toughest project yet. It’s the computing equivalent of the raising of the Mary Rose and they are up to challenge!

“We are very grateful to for becoming the first sponsor of the Harwell/WITCH computer restoration and we expect to be able to announce other sponsors soon.”

John Brooks of Insight Software said: “As designers of software that optimizes business processes, we are delighted to be the first sponsor of this restoration project. The Harwell/WITCH computer is a great early example of improving business processes – an objective that we as a company strive for today.”

The current earliest functioning computer is the 1956 Pegasus machine at The Science Museum in London. There are functioning rebuilds of earlier machines, including the Colossus Mk 2 at TNMOC.

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